Sample inlet systems for analytical instruments



Dec. 9. 1969 J, HARRIS, SR, ETAL 3,432,450

SAMPLE INLET SYSTEMS FOR ANALYTICAL INSTRUMENTS Filed 1967 2 Sheets-Sheet 1 Figum E H 14 24 I3 23 1Q 22'! 22 IIIIIIIIIIII m L CARRIER Dec. 9, 1969 J. HARRIS, SR. ETAL 3,482,450

SAMPLE INLET SYSTEMS FOR ANALYTICAL INSTRUMENTS Filed Dec. 1, 1967 v 2 Sheets-Sheet 2 Figwre 2 rr/ 1 l 1 o b 6 United States Patent 3,482,450 SAMPLE INLET SYSTEMS FOR ANALYTICAL INSTRUMENTS Rano J. Harris, Sr., and Rano J. Harris, Jr., Baton Rouge,

La., assignors to Precision Sampling Corporation, a corporation of Louisiana Filed Dec. 1, 1967, Ser. No. 687,179 Int. Cl. G01n 1/00 US. Cl. 73-422 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a new and improved inlet system, or adapter for an inlet system, for use in injecting fluid specimens or samples into analytical instruments.

Various types of inlet systems are described in the art for use in injecting gases and liquids, including high vapor pressure mixtures, into analytical instruments, e.g.

gas chromatographic analyzers, mass spectrometers, and the like.

The inlet systems to such analyzers are generally of tubular design with a more or less uniform cross-sectional internal area or volume. Such tubular sections generally provide (a) an internal volume, or chamber, wherein the sample is injected or removed from the injector or sampling device e.g., hypodermic syringe, pipette or the like, for transport into the analyzer; (b) an external volume, chamber, or entry feature which serves as a preliminary pumping stage or isolation chamber for the injector device; (c) a separating device to isolate the internal and external volumesor chambers (a) and (b)viz. a separating valve or septumand (d) carrier gas inlet means leading into the internal volume or chamber (a) for introduction or sweeping of the injected sample into the analyzer.

In such systems a heater is provided just adjacent the internal volume or chamber (a) for elevation of the temperature of the entering carrier gas and sample. The latter is generally volatilized or flashed by heating. The introduction of the sample, however, is not always smooth and instantaneous and there is some retention thereof within the internal chamber. Possibly, some of the sample enters into the external chamber or, in any event, tends to diffuse away from the mainstream of carrier gas. Release of the sample over an interval slows down the analysis and produces some erratic fluctuations in the readings. Moreover, the external chamber and auxiliary equipment become quite hot. This, inter alia, can be quite unpleasant for the operator who may occasionally touch the hot portions of apparatus in injecting the sample.

In accordance with the present invention, these and other prior art diificulties are obviated by use of a new and improved inlet system, or adapter for an inlet system. In accordance therewith, at least a portion of the external chamber of an inlet system is separated from the inlet chamber by a thin wall tubing with a small inside diameter which serves as a passageway. Carrier gas inlet means is provided at the side of the tubing near the external chamber so that carrier gas entering the inlet system, at relatively high velocity, will flow through the thin wall tubing toward the internal chamber. In the preferred manner of using such device, the injector or sampling device is inserted into the inlet chamber, a portion thereof ex tending through the thin wall tubing. The carrier gas is forced to enter the very small annulus between the external surface of the injector device and the inner wall of the tubing and, as sample is released by the injector device, it is swept into the internal chamber.

The invention will be better understood from the following more detailed description, taken in connection with the accompanying drawing, in which:

FIGURE 1 is a sectional elevation view of the overall combination; and

FIGURE 2 is a fragmentary view, in section, of the adapter portion with an injector or sampling deviceviz. a hypodermic syringe-inserted therein for delivery of a sample.

In the figures, there is represented a new and improved inlet system wherein an internal chamber 11 (FIGURE 1) is separated from an external chamber 12 by a septum 13, which isolates the two chambers one from the other. The internal chamber 11 of relatively large diameter or capacity, which leads e.g. to the column of a gas chromatograph, is provided with an extended portion or smaller chamber 14 through which carrier gas can be injected as via inlet 15. An electrical heater (not shown) generally surrounds chamber 11 to heat the carrier gas, and the injected specimen or sample.

A distinguishing feature of the invention relates to the thin walled chamber 14 which is of very low internal volume and which, in a very important sense, separates the external chamber 12 from the relatively large volume internal chamber 11. Significant features of this portion of the inlet system shall be described by further specific reference to FIGURE 2.

The portion of the inlet system associated with the relatively large volume internal chamber 11 can be considered an adapter-portion 10. The adapter-portion 10, in a convenient construction, is defined by a three-piece assembly which includes a member 22 which can be threadably secured to the member 23 via an externally threaded smaller end of shank 221 which mates with the internal threads of the extension 231 of member. 23. The member 22 is provided with a central opening or chamber 12 which terminates at the septum 13. Member 23 is provided with a recessed portion within which sets septum 13, and the latter can be held tightly and adjustably in place by the forward face of shank portion 221 of member 22. The channel 14 is formed by a thin wall comprising the tubular extension 24. of member 23. A carrier gas inlet 15 adjoins channel 14. Channels 14, 12, of generally similar diameter, are axially aligned and separated only by the septum 13. Additional supports (not shown) can be added to the structure, if desired.

In a typical and preferred type of operation, the needle 31 of a hypodermic syringe 30 can be thrust into the channel 12 of member 22, through septum 13 and into inner chamber 14 of tubular member 24. The penetrated septum clings tightly to the needle 31 to form a seal. Carrier gas can be injected into inlet 15 and forced to pass around the annulus created by the external surface of needle 31 and the inside portion of wall 24 of chamber 14. A measured sample injected via forward movement of plunger 32 will be swept by high-velocity carrier gas into the column of the analyzer since it cannot escape backward through the tight fitting septum or against the force exerted by the carrier gas.

By providing a very small total cross section through the annular opening, micro and semi-micro quanties of sample can be injected rapidly, quite smoothly, and with great precision. Because of the relatively high velocity of the carrier gas through the annular opening, there is essentially no diffusion of the sample. Further, due to the thin wall which forms tubular portion 24, heat is quite rapidly dlssipated, and there is little or no conductance through tubular portion 24. Thus, even where a temperature of 500'. to 600 C. is provided at the walls of chamber 11 the adapter portion will barely rise above room temperature. Readings can be taken quite readily, and there is little or no fluctuation.

In general, the internal diameter (or inside diameter) of the chamber or opening 14 ranges no more than from about 0.032 to about 0.25 inch, and preferably from about 0.040 to about 0.060 inch. The walls of tubular portion 24 range in thickness from about 0.005 to about 0.015 inch, and preferably from about 0.008 to about 0.012 inch, for the more conventional low-conducting, high-strength materials of constructions, e.g. ferrous metals, stainless steel, and the like. Of course, the walls can be thinner where lower heat conductance construction materials are used. In general, the length of tubular portion 24 ranges no more than from about one-half inch to about three inches, and preferably from about three-fourths to about two inches.

In injecting samples into a chromatograph it has been found suitable. to provide an annular difference between the external diameter of a needle, and the internal diameter of the walls of about 0.002 inch where about one and one-half to about 3 cubic centimeters per minute of carrier gas is injected to sweep sample into a column. An annular difference of about twice this dimension is employed to inject from 3 up to about 10 cubic centimeters per minute of carrier gas. An annular ditference'in diameter of about 0.009 inch is employed to inject from about 10 to about 50 cubic centimeters per minute, and an annular difierence of about 0.02 is employed to inject from about 50 to about 100 cubic centimeters per minute into a system. In general, it is desirable to increase the velocity of flow through the tubular portion at least about five times the normal velocity.

It is apparent that certain changes and modifications can be made without departing the spirit and scope of the invention.

What is claimed is:

1. In an inlet system to an analytical instrument wherein is included enclosing walls defining an external chamber,

an internal chamber,

an intermediate chamber connecting the said external and internal chambers,

a septum separating the external chamber from the intermediate chamber, carrier gas inlet means leading into the intermediate chamber, and

the improvement comprising a thin enclosing wall of thickness ranging from about 4 0.005 inch to about 0.015 inch forming the intermediate chamber,

the said thin enclosing wall forming the intermediate chamber providing a passageway of internal crosssectional diameter ranging from about 0.032 inch to about 0.25 inch, whereby carrier gas can be passed into the said intermediate chamber at high velocity to dissipate heat from the thin enclosing wall to maintain a cool external chamber.

2. The apparatus of claim 1 wherein the internal diameter of the intermediate chamber ranges from about 0.040 inch to about 0.060 inch.

3. The apparatus of claim 1 wherein the length of the intermediate chamber ranges from about one-half to about three inches.

4. The apparatus of claim 3 wherein the length ranges from about three-fourths inch to about two inches.

5. The apparatus of claim 1 wherein the wall of the intermediate chamber ranges from about 0.008 inch to about 0.012 inch.

6. The apparatus of claim 1 wherein the intermediate chamber is constructed of stainless steel.

7. The apparatus of claim 6 wherein the walls of the in termediate chamber ranges from about 0.005 inch to about 0.015 inch in thickness, and the length ranges from about one-half to about two inches.

8. The apparatus of claim 7 wherein the internal diameter of the intermediate chamber ranges from about 0.032 to about 0.25 inch.

9. The apparatus of claim 1 wherein the inlet system associated with the internal chamber comprises a first tubular member having a small diameter portion providing the intermediate chamber, an enlarged portion providing a receptacle for containing a second tubular member constituting the external chamber, and the septum is located between the second tubular member and the entry to the intermediate chamber.

10. The apparatus of claim 9 wherein the enlarged portion of the first tubular member is provided with an internally threaded extension, and the second tubular member with an externally threaded shank for threadable con nection one. member to the other.

References Cited UNITED STATES PATENTS 3,115,766 12/1963 Winters 73--23.l 3,327,520 6/1967 Stapp 7323.1

FOREIGN PATENTS 6/1964 Netherlands. 

